1. Field of the Invention
The present invention relates to a color light-sensitive material for use in photography, in which less deterioration in color balance in the case of photographing under different kinds of light sources occurs. More particularly, it is concerned with a color light-sensitive material for tungsten light, in which an extremely small deterioration in color balance in the case of photographing under a fluorescent lamp occurs.
2. Description of the Prior Art
Color films are used to take pictures under various light sources. However, the color balance of a color film, which is designed so that the best color balance can be obtained in photographing under a specific light source, is deteriorated when photographing using a different light source. This results from the difference in the distribution of light energy of the light sources versus wavelength. This also arises from the difference in color temperature of the light sources.
In recent years, color films have been widely used by amateurs. However, the photographing conditions vary widely. They are used under sunlight, tungsten lamp light or under fluorescent lamp light, alone or in combination. Since this color temperature of sunlight is very different from the color temperature of tungsten light, disadvantages occur when a color film which is designed to be the most suitable for photographing under a tungsten lamp light source (generally referred to as a tungsten-type color film) is photographed under sunlight. For example, the resulting positive image becomes bluish.
Whether the color balance when photographed under tungsten light source is strictly correct or not can be judged by photgraphing a neutral gray substance (a substance whose spectral reflectance or percent transmission is at a specific level over the entire visible wave-length region) under a tungsten light source and examining whether or not the position of the reproduced color on CIE standard chromaticity diagram (see Theory of Color Reproduction, pp. 10-26 and 160-162, translated by Tsutomu Mato and Taturo Kuniji, and published by Printing Society, 1971) coincides with the point corresponding to tungsten light on CIE standard chromaticity diagram.
In the case of photographing under mixture of light of a fluoroscent lamp and a tungsten lamp or under a fluorescent lamp light source, the color balance of tungsten-type color film is deteriorated and the value of the image is reduced.
In order to solve this problem, (1) a method of using light-sensitive materials appropriately designed to be suitable for different color temperatures and (2) a method of using a filter capable of converting the color temperature are known. For method (1), specifically, two types of light-sensitive materials have been manufactured for a long time: one type being for sunlight (referred to as a light-sensitive material for fluorescent color); and the other type being for a tungsten light source (referred to as a light-sensitive material for tungsten light). However, at the present stage since fluorescent lamps having various light characteristics exist and have been used even in comparison with a tungsten lamp, it is actually impossible to further increase the kinds of light-sensitive materials for proper use. Further, for method (2), although a large number of different kinds of filters can be used, the procedures of measuring the color temperature of a light source, selecting a suitable filter and attaching the filter to a lens are troublesome, and artificial errors such as incorrect selection of a filter and forgetting to employ the filter, and the like can not completely be prevented. As a countermeasure therefor, the incorporation of a mechanism for automatically converting the color temperature in a camera could be considered. However, such mechanism has the defect that the camera is large, complicated and expensive. An ideal method is to impart such characteristics to a color light-sensitive material itself so that it is not affected, or is affected only slighly, by a change in the color temperature of light source.
Some commercial products aiming at this effect are the reversal color films sold under the trade name of "Fujichrome RT 200" ("Fuji" being a registered trademark of Fuji Photo Film Co., Ltd.), and the like. In these products, the light-sensitive region of a red-sensitive layer is set on the shorter wavelength side as compared with ordinary color light-sensitive materials, the peak of optical sensitivity lying between 605 m.mu. and 640 m.mu. (usually set not shorter than 650 m.mu.). Although these light-sensitive materials are designed for tungsten light, their color balance is deteriorated less under fluorescent light as compared with ordinary color films. On the other hand, however, it is difficult with these light-sensitive materials to maintain the sensitivity level of the red-sensitive layer under a tungsten light source, because the light amount of red light component contained in tungsten light is decreased along the shorter wavelength side. This is because the amount of the red light component of tungsten light is decreased along the shorter wavelength side. Therefore, in order to maintain color balance under a tungsten light source, the sensitivity of the red-sensitive layer must be increased. However, where the size of the silver halide grains are increased to raise the sensitivity, the defect that the graininess of the red-sensitive layer is deteriorated occurs. Since graininess is one of the important elements for evaluating the image quality, the above-described defect is serious.